Brush assembly

ABSTRACT

A brush assembly has a base with a member to secure the base to a motor end cap assembly. A brush housing is associated with the base. The brush housing includes first and second open ends. A brush, defining an axis, is slidably supported within the housing. The brush extends from one of the first and second open ends. The brush includes a surface with a spring retention plunge. The spring retention plunge defines an arcuate face angled relative to the axis. A biasing member exerts a force directly on the arcuate face to bias the brush into contract with a commutator. An electrical connection is made between the commutator and a power supply.

FIELD OF THE INVENTION

The present invention relates to electric motors and more particularlyto brushes and brush assemblies implemented therein.

BACKGROUND OF THE INVENTION

Electric motors are used in a variety of applications, including powertools. Such electric motors generally include a motor shaft, a motorarmature, a field pole, field windings, a commutator assembly, brushholders and electrical leads. The electrical leads selectively linkbrushes to a power source. The motor armature is fixed for rotation withthe motor shaft and a series of copper conducting wires are wound invarious patterns about peripheral slits. Ends of the wires are fused tothe commutator. The commutator is fixed for rotation with the motorshaft and provides an electrical connection between the rotatingarmature and the stationary brushes. The brush holders each slidablysupport a carbon brush that is in sliding contact with the commutator.Generally, the stationary brushes are held in contact with an outsidesurface of the commutator by spring tension and complete the electricalcircuit between the rotating commutator and a power source.

Various spring biased mounting configurations have been developed tomaintain brush contact with the commutator. Effectiveness and weardurability of the brush is decreased when the brush is subjected toarcing. Arcing generally occurs as a result of the brush bouncing awayfrom the commutator as rough spots and irregularities of the commutatorpass under the brush. Prior art brushes include recesses formed thereinfor retaining an end of a biasing spring for effectively biasing thebrush in contact with the commutator. These prior art recesses, however,tend to be overly complex and thus more difficult to manufacture.Further, prior art recesses fail to prohibit lateral movement of thebiasing spring.

Therefore, it is desirable in the industry to provide an improved brushhaving a simplified recess. The recess should concurrently providesufficient biasing of the brush in contact with the commutator to avoidarcing and other detrimental occurrences.

SUMMARY OF THE INVENTION

A brush assembly is provided for implementation in an electric motor.The brush assembly includes a base with a member to secure the base to amotor. A brush housing is associated with the base and has first andsecond open ends. A brush, defining an axis, is slidably supportedwithin the housing between said first and second open ends. The brushextends from one of the first and second open ends. The brush includes asurface having a spring retention plunge. The spring retention plungehas an arcuate face angled relative to the axis. The brush assemblyfurther includes a biasing member exerting a force directly on thearcuate face to bias the brush within the housing to contact with acommutator. An electrical connector is electrically coupled with thebrush to electrically connect between the commutator and a power supply.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a perspective view of a motor including a brush assembly inaccordance with the present invention;

FIG. 2 is a perspective view of the brush assembly;

FIG. 3 is an exploded view of the brush assembly;

FIG. 4 is a plan view of the brush assembly in non-worn conditionrelative to a commutator shown in phantom;

FIG. 5 is a plan view of the brush assembly in a worn condition relativeto the commutator;

FIG. 6 is a perspective view of a brush of the brush assembly; and

FIG. 7 is a perspective view of a power tool implementing the motor ofFIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

With particular reference to FIG. 1, a motor 10 is provided and includesa frame 12, windings (not shown), a commutator 14, a brush assembly 16and a end cap 18. The brush assembly 16 is shown to couple with the endcap 18 and includes a base 20, a housing 22, a spring 24, a brush 26 andan electrical connection 28. The base 20 is preferably formed of anon-metallic or non-electrically conductive material and has a pair ofarms 30 to secure the brush assembly 16 to the end cap 18. Further, thebase 20 includes a web 32 which connects the two arms 30. The web 32 hasa recess 34 which receives the housing 22. The housing 22 is secured inthe recess 34 by tabs 36 which are bent under the base 20.

The housing 22 includes an open, tubular member 40 with a rectangularcross-section. The tubular member 40 has first and second open ends 42,44. The first open end 42 is positioned adjacent to the commutator 14when the brush assembly 16 is assembled onto the motor 10. First andsecond slots 46, 48 are positioned on respective sides of the tubularmember 40 and extend from the second open end 44. The slots 46, 48,respectively, enable the spring 24 and electrical connector 28 to movewith the brush 26. Also, a unitary shunt connection and connector 50 areformed with the housing 22. The connector 50 enables an electricalcontact 52 to be coupled with the housing 22. The shunt connection 50has a cutout 54 which interacts with a tab 55 to enable positioning ofthe housing 22 on the base 20.

The spring 24 is wound about a post 56 extending from the base 20. Thepost 56 may be angled off-center with respect to the axis of the base20. The spring 24 biases the brush 26 through the tubular member 40. Theelectrical connector 50 is known in the art and includes a pigtailconnector 51. An end of the pigtail connector 51 is ultrasonically orrestistively welded to the connection member.

The brush 26 includes a rectangularly cross-sectioned body portion 60with first and second ends 62, 64, respectively. The first end 62 has anarcuate face 66 having a series of ribs 68 (see FIG. 6). The ribs 68 arein sliding contact with the commutator 14 when the brush assembly isassembled onto the motor 10. The second end 64 includes a springretention plunge 70. The spring retention plunge 70 is a generallyconical-shaped depression, with a sloping, arcuate face 72 forming awall 74. A recess 76 is also provided and includes a surface where thepigtail 50 interconnects with the brush 26.

The slope S (see FIG. 4) of the arcuate face 72 of the spring retentionplunge 70 is preferably greater than 0 and less than or equal to 15degrees. It will be appreciated, however, that this range may deviate asdesign requirements dictate. The spring retention plunge 70 is formed toretain a contact end 73 of the spring 24. The contact end 73 isprohibited from moving along a lateral axis A (see FIG. 6) of the brush26. Likewise, the contact end 73 has limited movement along a transverseaxis B (see FIG. 4) of the brush 26. More specifically, the wall 74prohibits excessive travel of the contact end 73 along the transverseaxis B, in that direction. The slope of the spring retention plunge 70enables the contact end 73 of the spring 24 to ride within the springretention plunge 70 to provide constant contact with the brush 26.Ordinarily, the contact end 73 rides at the bottom of the arc. Thisconstant contact provides the force which, due to the slope, issubstantially constant during wear of the brush 26. The constant forceeliminates bouncing of the brush 26 and therefore increases the brushwear durability and prohibits damage to the commutator 14.

The spring retention plunge 70 of the brush 26 provides anotheradvantage in that it is more easily manufactured than prior art forms.More particularly, to form the plunge 70, a single step process may beimplemented, whereby a grinding wheel or round mill is plunged into thebrush 26 at an angle relative to the top face of the brush 26. Thegrinding wheel diameter, tilt angle and cut depth can be varied toprovide an optimum plunge 70. For optimization, the width and slope ofthe plunge 70 are considerations for the amount of play the spring 24will have while still biasing the brush 26. In this manner, manufactureof the brush 26 is variable and simplified and savings are achievable inboth cycle time and machine cost.

With particular reference to FIG. 7, an exemplary power tool 80 isshown, such as a power drill. The power tool 80 includes a housing 82having the motor 10 mounted therein, and an output member 84 in drivenengagement with the motor 10. A power supply, such as a power cord orbattery, is also included to respectively provide remote or local drivepower to the motor 10.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

What is claimed is:
 1. A brush assembly for an electric motor having an end cap assembly and a commutator, comprising: a base having a member for securing said base to the motor end cap assembly; a brush housing associated with said base and having first and second open ends; a brush, defining an axis, slidably supported within said housing between said first and second open ends, said brush extending from one of said first and second open ends, said brush including a surface having a spring retention plunge, said spring retention plunge defining an arcuate face angled relative to said axis on an angle greater than 0° and up to 15°; a biasing member having a contact end exerting a force directly on said arcuate face for biasing said brush within said housing for contact with the commutator, said contact end defining a line which extends across said arcuate face such that said contact end abuts said arcuate face along said line for prohibiting excessive movement of the contact end along an axis transverse to said brush axis; and an electrical connector electrically coupled with said brush for electrical connection between the commutator and a power supply.
 2. The brush assembly of claim 1, wherein said brush further includes a wall formed in said surface for retaining contact of said biasing member with said spring retention plunge.
 3. The brush assembly of claim 1, wherein a slope of said spring retension plunge enables transverse retention of said spring.
 4. A brush for an electric motor, comprising: a body having a desired configuration for fitting within a housing, said body defining an axis; and a spring retention plunge formed in a surface of said body, said plunge defining an arcuate face angled relative to a plane transverse to said axis, said surface at a terminal end of said body, wherein a slope of said arcuate face is greater than zero degrees and up to 15°, said arcuate face having a curvature sized to receive a spring such that the spring contacts the arcuate face along a line to prohibit excess movement of the spring on the arcuate surface for enabling spring force exerted thereon to be substantially constant as said body wears.
 5. The brush of claim 4, wherein said plunge further forms a wall in said surface for retaining contact of a biasing member with said spring retention plunge.
 6. The brush of claim 4, wherein said slope of said spring retention plunge enables transverse retention of a biasing member. 